抄録
This paper shows empirically that the income differential in Japan has increased in every age group since the end of the 1990s, using the micro data of 'National Survey of Family Income and Expenditure' (1999 and 2004) and 'Employment Status Survey' (1997 and 2002). About the increase in the income differential in the 1990s, the most influential view is that the population aging was the main reason for this increase. However, about the increase from the end of the 1990s, such view is denied by the result of this paper. In Section 1, we clarify that this increase occurred mainly in the wage income. Moreover, we explain an increase in the differential of consumption expenditure and saving. The wage income is a product of annual working hours and hourly wages. In Section 2, we analyse changes in annual working hours and hourly wages and shows that the differential of hourly wages of male regular employees has increased remarkably. In Section 3, we examine the reasons for an increase in the wage differential in regular workers, using 'Basic Survey on Wage Structure' and etc. This increase in Japan from the end of the 1990s was caused by the following three mechanisms. The first, the long stagnation and globalisation of Japanese economy led to a decrease in production and employment, which caused the drastic reduction in regular employees, combined with the non-regularization of employment. This reduction weakened the bargaining power of trade unions and led to the introduction of the performance-related pay system, which caused the polarization of wages. The second is the causation starting from deregulation. In the industries affected by the deregulation in the fields of transportation and distribution, the pressure of wage restraint has grown especially by the intensification of the competition among firms. The third is the causation regarding the Information Technology revolution, which raised wages of upper class workers in the IT sector. The fact that the number of these workers was limited denies the influential view that the main reason for an increase in wage differential is the skill change related to IT. The prospects of the wage differential in Japan are shown in Section 4. The mechanism of inter-firm wage equalization has been weakened by the deterioration of the spring labour offensive in Japan. Unfortunately, we can find no sign of the reversal of this trend. On the other hand, many Japanese companies are reconsidering the performance-related pay system because it often conflicts with the skill formation system. The equality in wages closely relates to workers' work effort and skill formation. As the company-based skill formation system in Japan cannot change quickly, the wage system must be suitable to it.
